This patent specification relates to the field of heat engines, and more particularly, to an Advanced Cheng Combined Cycle engine that combines features of the combined cycle and the Cheng Cycle or the Advanced Cheng Cycle.
A heat engine is a device that converts heat to work for the purpose of supplying power. There are many different applications of heat engines, ranging from small transportable engines to very large stationary engines. Typical applications include engines for automobiles, ships, aircrafts, and power plants. In steam, gas, or hydroelectric power plants, the device that drives the electric generator is the turbine. As the fluid passes through the turbine, work is done against the blades which are attached to the shaft. As a result, the shaft rotates, and the turbine produces work.
A gas turbine engine is a heat engine that is operated by a gas or liquid fuel rather than being operated, for example, by steam or water. The two major application areas of gas turbine engines are aircraft propulsion and electric power generation. When used for aircraft propulsion, the gas turbine produces just enough power to drive the compressor and to drive a small generator to power the auxiliary equipment. The high-velocity exhaust gases are responsible for producing the necessary thrust to propel the aircraft.
In the application area of electric power generators, gas turbines are used as stationary power plants to generate electricity. Gas turbine power plants are mostly utilized in the power generation industry to cover emergencies and peak periods, because of their relatively low cost and quick response time. With the deregulation of public utilities, systems must attain peaking power during working hours to follow the load profile of electrical consumption.
Three well-known cycles for heat engines relating to gas turbines are the combined cycle, the Cheng cycle, and the Advanced Cheng cycle. FIG. 1 is a block diagram of a typical combined cycle. The combined cycle is a combination of a gas turbine cycle (known in the art as a xe2x80x9cBraytonxe2x80x9d cycle) and a steam turbine cycle (known in the art as a xe2x80x9cRankinexe2x80x9d cycle) in series.
The waste heat from the gas turbine cycle is used to boil the water in the separate steam cycle. A working fluid is a fluid to and from which beat is transferred while undergoing a cycle. The combined cycle has separate loops for two working fluids with two separate and distinct power turbines. The two working fluids are not mixed, unlike in the Cheng cycle as will be explained below. Although steam generated from the exhaust waste heat of a gas turbine powers the combined cycle, very high pressure at a low temperature is used to economically drive a conventional steam turbine and its associated accessories.
The combined cycle may include a single gas turbine or multiple gas turbines. Exhaust from the gas turbines is directed into a Heat Recovery Steam Generator (HRSG), which produces an intermediate amount of pressurized steam (greater than 1000 pounds per square inch absolute or psia) at a temperature greater than 750 degrees Fahrenheit (F), which is used to drive the steam turbine. The steam is then condensed by a condenser and recycled back into the boiler. Heat is rejected from the condenser by means of a cooling mechanism, usually a cooling tower.
Both the Cheng Cycle and the Advanced Cheng Cycle were conceived by the Applicant of the present invention in the 1970s, and one or both have been the subject of a number of prior art patents, including U.S. Pat. Nos. 3,978,661, 4,128,994, 4,248,039, 4,297,841, 4,417,438, and 5,233,826, which are hereby incorporated by reference.
The Cheng Cycle engine is a dual-fluid engine which makes use of two separate working fluids. Each fluid is compressed separately, but they are combined in a single mixture for expansion and heat regeneration. This cycle essentially combines a Brayton cycle and regenerative Rankine cycle system in parallel such that operational limitations of compression ratio in the Brayton cycle, upper temperature in the Rankine cycle, and waste heat rejection in both cycles are removed or reduced. An important feature of this cycle is regeneration using the Rankine cycle working fluid.
FIG. 2 is a block diagram of the Cheng Cycle, which, like the combined cycle, comprises a gas turbine. A heat recovery steam generator (HRSG) also recovers the Cheng Cycle""s exhaust waste heat, but usually at a lower pressure (under 1000 psia) and at a much higher steam temperature. The generated steam is then injected back into the gas turbine through a combustion chamber, which has downstream turbine stages that include both power augmentation for the turbine and cooling for the high temperature components. After undergoing these processes, the gas turbine exhaust comprises both air and steam. This additional steam will allow the Heat Recovery Steam Generator (HRSG) to generate more steam than normal gas turbine waste heat can produce alone.
FIG. 6 illustrates the components associated with an embodiment of the Cheng Cycle. The gas turbine has a compressor 10 linked to a turbine 13 by shaft and output to a load. The air intake through compressed air port 1 is compressed and then discharged at 2. The compressed air enters a combustion chamber 12. Fuel enters the combustion chamber through port 11, and steam comes from the heat recovery steam generator (HRSG) to port 3. The mixing of the combusted air and steam reaches a predetermined turbine inlet temperature, then discharges from outlet 4 through turbine 13, exiting the turbine at outlet 5. Exhaust gas then passes through the heat recovery steam generator, which is divided into two parts: a superheater 14, and a water-to-steam generator 15. The hot exhaust gas enters the superheater 14, gives up the heat to superheat the steam entering at 8 and exiting at 3. A duct burning capability is not depicted here, but would normally be located at 6. The remainder of the heat is recovered by the unit evaporator 15 and exits at valve 17. The exhaust gas at 7 has the option of going through a cleanup or condensing unit 20, then to the atmosphere. Water can be recovered through 20 or can be totally used as a makeup entering or mixing with 19. Water is compressed to a high pressure through a pump 18. The pump exit goes into the steam generator at 9, and the evaporator controls the steam flow by two valvesxe2x80x9416 into the superheater, and 17 into a congeneration unit (not shown).
Therefore, as can be seen from the foregoing description, the Cheng Cycle is a steam-injected gas turbine that uses steam generated by recovering the waste heat of the gas turbine. A predetermined mixture of air and steam, in an appropriate functioning ratio, defines the contour of a partial load operating line. As demonstrated in the industry, the Cheng Cycle is extremely simple to implement, with high levels of efficiency and dynamic response.
The Advanced Cheng Cycle represents an improvement over the Cheng Cycle. A difference between the Cheng Cycle and the Advanced Cheng Cycle is that in the Advanced Cheng Cycle, steam cooling is bled into the gas turbine. This process does not occur in the Cheng Cycle. At the time the Cheng Cycle was conceived, the majority of gas turbines were operating at a metallurgically tolerable turbine inlet temperature for stress and corrosion protection. The Cheng Cycle was therefore conceived at that time without consideration to cooling of the turbine blades.
Although the combined cycle and the Cheng Cycle or the Advanced Cheng Cycle provide many benefits as described above, improvements are still desirable. For example, it would be beneficial to increase the power output of the combined cycle, especially during the day in the summertime. It would also be beneficial to reduce the NOx emissions of the combined cycle. Further, it would be helpful to provide dynamic load-following capabilities so that systems may optimally attain peaking power during working hours.
One object of the disclosure herein is to increase the power output from that of a combined cycle, especially during the day in the summer time. Another is to reduce the NOx emissions typical in the combined cycle. Yet another is to provide dynamic load-following capabilities.
These and other objects are accomplished by effectively combining features of the Cheng Cycle or the Advanced Cheng Cycle with the combined cycle to form the Advanced Cheng Combined Cycle. The Advanced Cheng Combined Cycle realizes power-producing capabilities that surpass those of the combined cycle. It also exhibits characteristics that surpass the well-established baseload work characteristics of the combined cycle. Furthermore, it provides load characteristics even more flexible than the load-following characteristics of the Cheng Cycle or the Advanced Cheng Cycle.
The present specification discloses in one embodiment an Advanced Cheng Combined Cycle system. A gas turbine is provided, having a turbine generating power, a compressor receiving power from the turbine, and a combustion chamber to which is input compressed air from the compressor along with fuel and combustion products for producing energy to drive the turbine, the gas turbine producing a hot stream gas. A heat recovery Steam generator receives hot stream gas produced by the gas turbine and generates high-pressure steam therefrom. A steam turbine receives and is driven by high-pressure steam generated by the heat recovery steam generator. The steam turbine bleeds intermediate-pressure steam for cooling the turbine and for injection back into the combustion chamber of the gas turbine. A control valve throttles down high-pressure steam generated by the heat recovery steam generator to a low-pressure steam for injection back into the combustion chamber of the gas turbine.
The heat recovery steam generator may further comprise a duct burner for increasing the temperature of hot stream gas produced by the gas turbine to produce additional steam for injection back into the combustion chamber of the gas turbine.
The Advanced Cheng Combined Cycle system may further comprise an emission control system disposed between the gas turbine and the heat recovery steam generator.
In the operations of the Advanced Cheng Combined Cycle, according to the preferred embodiments, the duct burner is added to the combined cycle to generate additional steam for injection into the gas turbine. The injected steam increases the mass flow level of the gas turbine to facilitate production of additional steam. As a result, the waste heat boiler, known as the Heat Recovery Steam Generator (HRSG), is capable of producing more steam at a higher thermal efficiency level. The thermal efficiency level represents the fraction of the heat input that is converted to net work output, and therefore measures the performance or efficiency of the engine.
Because the additional steam generated by the duct burner makes the gas turbine power augmentation much more flexible than that of the combined cycle alone, the Advanced Cheng Combined Cycle can perform load-following during the day and perform baseload work in off-peak hours. The steam injection also reduces NOx emissions at an extremely low cost.